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Long ago, a giant pillar of hot, molten rock from deep within the
Earth may have played a role in the extinction of the dinosaurs
by triggering massive volcanic explosions. That deep jet of magma
may still be around, and researchers are now deploying a vast
array of electronics on the seafloor to try to learn more about
it and the effects it can have on Earth's surface.

A French-German expeditionis currently exploring the source of
volcanism at Réunion Islandin the Indian Ocean. Unlike most
volcanoes, the earthshaking activity here doesn't occur at the
border of colliding tectonic plates, but instead arises within a
tectonic plate.

"Réunion is one of the most suitable places on Earth to
investigate the problem of
intra-plate volcanism in the oceans," said researcher Karin
Sigloch, a seismologistat Ludwig Maximilian University of Munich.

The source of this volcanic violence is a so-called hot spot that
apparently has roots at great depths — a titanic
jet of magma known as a mantle plume that pumps colossal
amounts of heat upward, burning through the overlying material
like a blowtorch.

As the millennia have passed andEarth's surface has drifted over
this mantle plume, it has seared a track of volcanic activity
that stretches about 3,400 miles (5,500 kilometers) northward
from Réunion to the Deccan Plateau region of what is now India.
At the
end of the Age of Dinosaurs about 65 million years ago,
massive volcanism in the Deccan area spewed lava across 580,000
square miles(1.5 million square km), radically altering Earth's
climate and potentially hastening the giant reptiles’ demise.

To help resolve the controversy, the expedition is deploying
nearly 60 seismometers on the floor of the Indian Ocean over a
vast area of about 1.5 million square miles (4 million square
km). They will install more instruments on land at
Réunion,Mauritius, Madagascar and the Seychelles, while other
observatories around the Indian Ocean coastline will contribute
data, making this project the largest campaign ever to map a
mantle plume.

"In all, there will be about 180 broadband seismometers running
in our area of interest during this coming year," Sigloch told
OurAmazingPlanet. "We want to look deeper into the Earth's
interior than any previous expedition, down to the bottom of
the mantle at a depth of about 2,900 kilometers [1,800 miles] —
earlier efforts reached half that depth, at most."

The seismometers deployed on Réunion may also help protect the
island's residents. "We do expect to learn more about currently
active and dangerous volcanism there, and perhaps also the
potential for gigantic landslides and tsunamis when half of the
volcano slides into the sea, which can happen, though it's very
unlikely," Sigloch wrote via email from aboard the French
research vessel Marion Dufresne.

The seismometers the researchers are dispersing in the ocean are
each about 3 by 4 by 2 feet (1 by 1.2 by 0.6 meters) in size and
weigh about 570 pounds (260 kilograms). Powered by lithium
batteries, they will record seismic data for 13 months.

Fishing for seismometers

To gather data, the researchers lower the seismometers to the
seabed — which can vary from 7,500 feet (2,300 m) to 18,000 feet
(5,500 m) deep in the study area — by dropping them off the side
of the boat with a crane. [ Infographic:
Tallest Mountain to Deepest Ocean Trench ]

"Then [the seismometers] sink to the ocean bottom within an hour
or two … hopefully onto a not-too-rugged spot," Sigloch said. A
heavy, iron anchor then ensures the devices sit solidly on the
ground.

In a year, the scientists will return to collect each seismometer
with the German research vessel Meteor. They will bounce acoustic
pings off the seismometers, prompting the buoyant part of the
seismometer to detach from the anchor and rise, with all its
data, back to the surface. The acoustic pings will help the team
locate the devices.

"It becomes a fishing expedition. You need to spot it — not
always easy, but easier at night, because it has a flashing
device," Sigloch said.

"When everything goes well, a recovery takes two to three hours.
When the weather is very bad and the waves are high, it may not
be possible to recover at all."

The research cruise began Sept. 27, five days later than planned
due to a port worker strike, and is scheduled to finish at the
end of October. Once the
seafloor seismometers are recovered in 2013, the scientists
hope to create 3-D pictures of the mantle plume from the crust to
the core.

It remains uncertain whether even a project this large will
completely image the mantle plume. "We don't know exactly how
large, strong, deep [or] where it is," Sigloch said.